1. Field of the Invention
This invention relates to helicopter rotors and more particularly to helicopter rotors which are retractable so that the helicopter may be flown with the main lift rotor positioned a sufficient distance above the helicopter fuselage to avoid high air turbulence therebetween in forward flight, which turbulence would add to the helicopter drag and reduce its forward speed and reduce the vibration levels of the aircraft, and which can be retracted to a position closer to the fuselage for transportation of the helicopter in another vehicle.
2. Description of the Prior Art
In the helicopter field, there are the requirements that the main lift rotor be positioned a sufficient distance above the helicopter fuselage in flight so that coaction between the two does not establish vibrations and drag and, also, that the helicopter rotor can be retracted and secured in a position close to the fuselage when the helicopter is to be transported in another vehicle, such as a larger aircraft, an aircraft carrier, or a land vehicle.
Retractable rotors are known, principally in the converti-plane art wherein the entire rotor and its drive mechanism, such as the transmission and drive shafts, are retractable and extendable with respect to the fuselage. Experience has shown that such mechanisms are complicated in nature, heavy in weight, and occupy large volumes of space both within and outside of the fuselage thus resulting in increased frontal area and reduced cargo or passenger capacity. Examples of such constructions are shown in U.S. Pat. No. 3,370,809. During the evolution of our invention, this approach was thoroughly analyzed and found unacceptable for the reasons stated above.
Other known constructions in the helicopter art permit retraction of the helicopter rotor but require that all blades be removed prior to retraction, and this was found to be unacceptable because of the time factor involved to prepare the helicopter for air or other transportation and thereafter for operational flight again.